Developing large electrical/electromechanical systems and devices, with multiple, components drawing significant power loads, can require many man hours of testing and a significant amount of money to insure that the system or device is operating within the desired specifications. To reduce testing time and expenses, engineers will often emulate the power drawn or consumed by system components under various conditions. Linear, non-pulsing loads have no switching and, therefore, draw current with a linear relationship to the voltage. Consequently, the power drawn from linear elements is relatively easy to emulate.
However, most electronic elements are non-linear loads, which can have current that is leading or lagging the voltage. Consequently, there is an inverse relationship between the current and voltage. That is, current increases as voltage decreases, and vice versa. A non-linear load can create instantaneous rates of change in the current. When this happens, the circuit output is choppy and non-sinusoidal. These switching circuits cause distortion in the power which is very problematic when trying to emulate the power drawn by these loads. This emulation is increasingly more challenging when additional non-linear components are added. When components are added, engineers need to account for fluctuations in power consumption due to device performance characteristics, environmental changes, and the like.
Silicon Controlled Rectifiers (SCRs) based on inductor-resistor (LR), or inductor-resistor-capacitor (LCR) circuits are used to emulate the power drawn from loads in electronics systems. Typically SCRs are four-layer solid state current controlling devices with 3 terminals. Like conventional diodes, SCRs have an anode and cathode terminal. They also have a third control terminal, referred to as a gate. SCRs are unidirectional devices (i.e. they conduct current in only one direction like a diode or rectifier), and are triggered only by currents going into the gate. SCRs combine rectifying features of diodes and the switching ON-OFF control features of transistors.
In their normal OFF state, SCRs restrict current flow to the leakage current. When the gate-to-cathode current exceeds a certain threshold, the device turns ON and conducts current. SCRs remain in the ON state even after the gate current is removed so long as the current through the device exceeds the holding current. Once the current falls below the holding current for a period of time, the device will switch off. If the gate is pulsed and the current through the device is below the latching current, the device will remain in this OFF state. Because of this feature, SCR circuits can be made to control the mean value of an AC load current without dissipating large amounts of power. Therefore, they are used in a variety of applications including AC motor-speed control, temperature control systems, and power regulation circuits, etc.
The drawback of these types of SCR systems is that they are not computer programmable and thus lack emulation accuracy. System engineers need the flexibility to program systems with specific power specifications to accurately mimic the power drawn by particular loads.
Currently, power loads are emulated by utilizing multi-phase resistors that are turned on and off to mimic load signatures. Alternatively, other known systems have utilized a circuit system with multiple loads, wherein one of the loads is always on and drawing a particular voltage and the other resistive load is switched on and off to emulate a load. However, these solutions are problematic because resistive loads will automatically turn on at certain current thresholds, making it impossible to program the system. Consequently, this invention allows engineers to apply an actual known voltage load with a converter and control the timing of the system to more accurately emulate electronic power signatures.
One situation where this emulation accuracy is really needed is in aircraft testing. Typically the most accurate way to test aircraft systems is in-flight, which is time consuming and very expensive. This is particularly true with military aircraft. In addition to the time and expense, there is the additional concern of flight test safety. Therefore, engineers prefer to perform tests on land prior to, or in lieu of, conducting in-flight testing to reduce costs and maximize the safety of the flight crew. Aircraft contain many electronic systems (such as, but without limitation, radar, navigation, and communications equipment) that draw significant power in varying amounts depending on the conditions in which the aircraft is being flown. This makes replicating the power signature of an aircraft particularly difficult.
In addition, military aircraft have highly technical tactical and weapon systems and are designed to execute advanced maneuvers in extreme conditions requiring additional performance from their systems' components. These features and requirements create additional requirements and fluctuations to the power signature of the aircraft's systems.
Consequently, it is critical that engineers are able to accurately emulate the power drawn by aircraft components under these conditions to obtain more accurate testing results to identify system needs and capabilities. Therefore, there is a need for a programmable system that can match component power specifications and more accurately emulate power consumption of the electronic systems.